This invention relates to honeycomb grilled conduits of the type used for vacuum applications such as the drying of a paper web.
Honeycomb grilled conduits of the indicated type generally comprise a channel to which a vacuum is applied and a honeycomb grill extending across the open portion of the channel. A vacuum is applied to the interior of the channel to draw the drying medium through the web to be dried and the honeycomb grill. In use, a plurality of the conduits are placed in side-by-side relation to provide an extended drying surface with the sidewalls of adjacent channels extending alongside one another. By reason of this arrangement, a dividing line is formed where the channels are joined because in the present-day grilled conduits the honeycomb grill is mounted to be flush with the end of the channel on which it is supported. The result is that there is formed a blind spot to the flow of drying medium being drawn into the interior of the channels by reason of the vacuum applied thereto. This blind spot is located along the dividing line where adjacent conduits are mated to form the extending drying surface. This leads to drying nonuniformities and hence undesirable web properties such as cockling and scorching. Cockling is the fault due to differences in tension set up during drying whenever the drying rate is different in one portion of the web to adjacent portions. Scorching is caused by overdrying portions of the web in order to reduce peak moisture areas. Overdrying causes the web to heat up to the supply air temperature thereby causing discoloration of the web by oxidation.
It is the general object of the invention to provide a honeycomb grilled conduit of the indicated type which eliminates the blind spot formed at the location where adjacent conduits mate.
Briefly stated, the general object of the invention is achieved by the provision of a grilled conduit means which comprises a plurality of conduits each of which includes means providing a channel having a pair of spaced apart sidewall portions defining a channel opening, the channel having a passage through which a vacuum can be applied to the interior of the channel. Each conduit also comprises a honeycomb grill extending across the channel opening between the outer edges of the sidewall portions, the honeycomb grill having a plurality of open cells therein for the flow of the drying medium into the interior of the channel. The plurality of conduits are mounted in side-by-side relation with sidewalls of adjacent conduits being juxtapositioned to provide a dividing line region therebetween and an extended drying surface. Pursuant to the invention, the honeycomb grill of each conduit is raised outwardly of the edges of the sidewall portions to provide between adjacent honeycomb grills an open flow area for the flow of the drying medium in the dividing line region beyond the sidewall edges of juxtapositioned sidewall portions. By this construction a continuous drying surface is provided.